1. Field of Invention
The invention relates to a method of focus balance calibration, and more particularly to a method for pre-calibrating a balance gain of an analog front end by way of offline calibration.
2. Description of the Related Art
In the prior art, the frequently used focus balance calibration performs the compensation according to level balanced displacement amount (Focus Balance DAC) on the focus balance but without the consideration of a balance gain of an analog front end. So, this method is not stable enough and cannot compensate for the larger variation. FIG. 1 is a schematic illustration showing shapes of light beams projected onto an optical head according to the prior art, wherein state 1 shows the shape of the light beam before compensation, and state 3 shows the shape of the light beam after a level balanced displacement amount on the focus balance is compensated. As shown in the state 1 of FIG. 1, when each optical pickup and a circuit board and a thickness of a disk material make the focus balance have the larger variation, it cannot be simply compensated according to the level balanced displacement amount on the focus balance, and only the compensated result of the state 3 of FIG. 1 can be obtained.
Therefore, if the focus balance gains A, B, C and D of the analog front end can be further adjusted to compensate for the influence of the focus balance caused by the optical pickup and the circuit board, then the optimal power calibration (OPC), the successful disk-reading possibility, the write-in quality and the stability of the disk judging mechanism can be enhanced, and the consistency and the stability of the product can be improved.